1. Field of the Invention
This invention relates to a method for manufacturing magnetic heads having both magnetoresistive and inductive elements and to the products of the process.
2. Description of the Prior Art
The conventional technique for both reading and writing data recorded as magnetic manifestations on magnetic tape has been the inductive magnetic head. In such a head, a single inductive winding has been provided for each track on the head. Electrical current in a winding causes a magnetic field which records magnetic manifestations on the tape corresponding to the electrical current. During reading, the same winding detects recorded magnetic manifestations and translates them into corresponding electrical voltage. Simultaneous reading and writing normally requires two windings per track to prevent the current in the write winding from causing an undesirable voltage in the read winding. Recently, the magnetoresistive element has been recognized as an especially good read element capable of replacing an inductive winding. However, the magnetoresitive element is also sensitive to magnetic fields emanated by write inductive windings and must be shielded from inductive and capacitive coupling with the windings.
In an article entitled "Magnetoresistive Read/Write Head", by G. W. Brock, F. B. Shelledy and L. Viele, appearing in the IBM TECHNICAL DISCLOSURE BULLETIN, pages 1206-1207, September, 1972, there is described a read-while-write magnetic head comprising a magnetoresistive element and a conductive write inductor placed within the same gap formed by two ferrite poles. The cross-talk or feedthrough between the inductive winding and the magnetoresistive element is reduced in this configuration by pulse thing. Placing the magnetoresistive element between two conductors forming the inductive winding, as described in U.S. Pat. No. 3,887,945, entitled "Head Assembly for Recording and Reading, Employing Inductive and Magnetoresistive Elements", by D. A. Nepela et al, issued June 3, 1975, and assigned to International Business Machines Corporation, isolates the read and write elements from each other. The cross-talk may be reduced and the isolation between the inductive element and the magnetoresistive element increased by providing shields between the element, constructed of Permalloy, as described in patent application Ser. No. 498,504, entitled "Integrated Magnetoresistive Read, Inductive Write, Batch Fabricated Magnetic Head", by L. t. Romankiw, filed Aug. 19,1974, now U.S. Pat. No. 3,908,194 and assigned to International Business Machines Corporation. The use of a highly conductive material to reduce feedthrough from the write field to the read element is suggested in a paper presented by G. W. Brock and F. B. Shelledy, Apr. 15, 1975, at the 1975 INTERMAG Conference, London, England, entitled "BAtch-Fabricated Heads from a Functional Standpoint".
In addition to the need to reduce feedthrough of the write field to the read element, the last referenced article discusses the criteria necessary for a magnetic head to operate in the read-while-write mode. Such a magnetic head requires special manufacturing processes and materials characteristics in order to operate properly and, in fact, to be capable of construction at all. When the elements are placed onto a substrate by thin film deposition techniques prior to assembly into a magnetic head, the problems are multiplied. For example, it is necessary to lap the substrate material to a sufficiently high finish and flatness, in order to obtain optimum magnetoresistive properties in the element, and simultaneously form and contour the head materials to a correct and accurately determined air bearing surface. The surface must then be continuously and uniformly wear-resisting and free from thin, soft lines of material transverse to the tape path and from any pockets that can suffer from erosion and subsequent filling with debris. The contour surface must, further, be free from materials that cause adhesive wear of the tape surface and, hence, contaminate the contour. Insulation problems must be avoided during manufacture and operation. A low running temperature must be maintained in order to avoid head stability problems and contamination of the head surface by the media. In conventional methods of packaging such heads, the deposited elements are sandwiched between two hard materials, leaving an empty space between adjacent elements which is normally filled by epoxy-type cements. However, the epoxy line which appears on the contour of the magnetic head after contour formation is eroded by the media faster than the surrounding, usually metallic, material. This leads to contaminaton of the epoxy line by debris. Another problem that results from this approach is the presence of a portion of the element itself at the surface of the head during contouring. Since the element is usually a soft material such as copper while the rest of the head is some harder material, the finishing operation results in smearing of the soft metal, chipping of insulation layers and damage to the harder material because of contamination of the finishing machine cutting tools by the soft metals. Smearing can cause undesirable electrical shorts, and the mere presence of the copper in contact with another metal can cause corrosion by electrolysis.